1. Field of the Invention
The invention relates to a method of treating a well penetrating an unconsolidated formation from which detritus is carried into the well with produced fluids, i.e., a well penetrating a formation referred to in the art as being "incompetent".
2. Description of the Prior Art
Production of detritus from unconsolidated, i.e., incompetent, subterranean formations producing valuable fluids, such as production of sand from an incompetent sand stone formation, is an ever present problem, particularly in the petroleum industry. A good discussion of the problem, and of the various techniques used to minimize concurrent production of such detritus, can be found in an eight part series by George O. Suman, Jr., appearing in World Oil from November, 1974 through June, 1975. The series was published in 1975 as a reprint by Gulf Publishing Company under the title "World Oil's Sand Control Handbook". Three commonly used methods are (1) gravel packing, (2) plastic in situ consolidation, and (3) consolidated packing with a particulate material, often called consolidated gravel packing especially where the particulate material is sand. The latter two methods are discussed in Part 7 of said Handbook, the teachings of which are expressly incorporated herein.
Generally, in forming a consolidated pack of particulate material, a slurry containing a carrier fluid, particles of the solid material, and at least one adhesive-forming composition, such as a resin, for permeably but stably adhering the particles together is injected into the borehole. The slurry may contain complete means for permeably but stably adhering the particles to one another, as where the adhesive-forming composition requires no chemical activator such as a curing agent or catalyst, or where any necessary activator is also provided as part of the slurry. Alternatively, where the adhesive-forming composition must be chemically activated and the activator is not provided in the slurry, the prior art has provided the activator in an injection either immediately before, or immediately after, injection of the slurry.
Although the art of forming consolidated packs of particulate material has advanced considerably over the past 20 years or so, the prior art methods are not always completely satisfactory for the job at hand. For example, strong, long lasting gravel packs could not be obtained with consistency adjacent incompetent formations having a relatively high porosity and low pressure by previously known methods as heretofore practiced.
A separate art in the treatment of wells relates to the use of temporary self-breaking plugs. The temporary plug is formed from a fluid which forms a gel. The fluid may be one from which a gel is formed at the surface of the earth and the gel is then pumped into the formation under relatively high pressures, or, the fluid may be of a type which reaches its maximum viscosity after injection into the borehole. In either case, after a period of time sufficient to carry out additional treatment of the well, the gel breaks so that the remains of the gel can readily be removed from the formation. An example of such a system is taught by Nimerick in U.S. Pat. No. 3,615,794. Such a temporary plug has been used in penetrating formations having zones of different permeabilities to divert a subsequent well treatment fluid of lower viscosity into less permeable zones to thereby obtain more uniform treatment of the formation, e.g., in conjunction with fracturing, water flooding, or acidizing.
In the context of sand control, a temporary plug has been used with plastic in situ consolidation in the conventional sense, i.e., as a diverter. See Smith, U.S. Pat. No. 3,250,330 at columns 11 and 12. Robichaux, U.S. Pat. No. 3,123,138 teaches to use a temporary plug in conjunction with plastic in situ consolidation following, rather than preceding, injection of the resin to cause a sharp increase in pressure at the well head when the plug reaches the formation, thereby signaling when all of the resin has entered the formation.